Coordinate Systems for the Earth Surface
From Ocean Teacher Library
Contents |
Background
Coordinate systems are the various methods used to specify individual points on the surface of the earth, using the chosen datum as the physical basis. The commonly found systems are reviewed by Dana in the reference below. Of particular interest to marine science are these:
Geodetic or Geographic or "Common" Reference System (GRS)
This is the familiar global geographic coordinate system of latitude, longitude and altide, based on these principles:
- The equatorial plane
- The prime meridian plane
- Latitude of a point near the earth is the angle between the equatorial plane and a line passing through the point, normal (perpendicular) to the ellipsoid surface
- Longitude of a point on the surface is the angle between the plane of the prime meridian and a plane containing the point, if both planes are normal (perpendicular to the equatorial plane
- Height is the distance from the ellipsoid to the point, along a line normal (perpendicular) to the ellipsoid
- There are other less common constructions of, for instance, latitude. These latitudes are listed in the Wikipedia article referenced below: Reduced, Authalic, Rectifying, Conformal, Geocentric
- More detailed information and practical examples of latitutude and longitude are found in Geolocation by Latitude and Longitude
Universal Transverse Mercator (UTM)
In this system, well described in the Wikipedia reference below, the world between latitudes -80 and +84 is divided into north-south (given identifying numbers) and east-west zones (given identifying letters)., and within each zone positions are designated by measurements from the north-south center line and the equator. The north-south zonation scheme is far more commonly used.
- There are 60 6-degree-side north-south zones, beginning with Zone 1 (-180 longitude to -174 longitude) and continuing east to encircle the globe. These zone numbers when stated in coordinate references (e.g. UTM 14) uniquely identify their location. Note that some special-numbered and letters zones also exist.
- In numbered zones, east-west measurements ("eastings") are given as meters east of the north-south center line plus 500 km to eliminate negative numbers. North-south measurements ("northings"), also in meters, are similarly increased by 10,000 km.
Coordinate Reference Systems (CRS)
Regardless of coordinate system selected for use, the physical model of the earth on which the coordinate system operates must also be specified. This results in a Coordinate Reference System (CRS), as discussed in a separate article.
Additional Resources
Subsections of this article
| Pagename | Short title | Description | |
|---|---|---|---|
| Coordinate Reference Systems (CRS) | Coordinate Reference Systems (CRS) | Coordinate Reference Systems (CRS) | none |
| Geolocation by Latitude and Longitude | Geolocation by Latitude and Longitude | Lat/Lon Geolocation | none |
| Non-Standard Latitude-Longitude Notations | Non-Standard Latitude-Longitude Notations | Non-Standard Latitude-Longitude | none |
Information about this article
Short title: Coordinate Systems
Description: none
Expertise level: beginner
Author: Murray.Brown
Approval status: approved
Approved by: Murray.Brown
Last change: 2009-9-1
Subsection of: Geospatial Data Concepts
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